PST, or Pacific Standard Time, is a time zone that is 8 hours behind Coordinated Universal Time (UTC-8). It is primarily observed in the western regions of the United States and Canada, including states like California, Washington, and Oregon. PST is used during the fall and winter months when Daylight Saving Time is not in effect. When Daylight Saving Time begins in the spring, PST shifts to Pacific Daylight Time (PDT), which is UTC-7. This change typically occurs on the second Sunday in March and reverts back on the first Sunday in November. The use of PST helps standardize time across different regions, facilitating scheduling and communication.